The present invention relates to a motion sensor assembly. More particularly, the present invention relates to an infrared motion sensor assembly for use as a lamp switch. The motion sensor assembly is mounted adjacent an opening in a housing such that the assembly is concealed from view within an interior space of the housing. An infrared detector of the motion sensor assembly outputs a signal responsive to infrared energy radiated from a source present in a field of view of the motion sensor assembly. A circuit of the motion sensor assembly provides a signal in response to the output signal of the detector. The motion sensor assembly also has a transformerless direct current power supply.
Some research has shown that lighting can account for between 30% and 50% of the electric costs of a facility. Shutting off lights when they are not needed can reduce these costs. However, people often cannot or forget to turn off facility lights they are not using.
An infrared motion sensor assembly could be used as an on/off switch to control lighting of a facility. A field of view of such an assembly could, for example, cover a work area such as a desk. When a person moved toward a work area, he or she would radiate infrared energy that would be detected by the motion sensor assembly. The assembly could switch on lighting for use by the person when at the work area. After the person left the work area, infrared energy would no longer be radiated and detected by the motion sensor assembly. The assembly could switch off the lighting for the work area in order to conserve electric energy and thereby reduce facility costs.
Infrared motion sensor assemblies are known. Such assemblies have found application in such things as security devices. See, for example, U.S. Pat. No. 4,734,585 to Owers for a Passive Infra-Red Sensor. Current infrared motion sensor assemblies are often obtrusive and unattractive in appearance. Use in such environments as an office may be undesirable.
Infrared motion sensor assemblies, however, are not readily concealable from view because light must be able to enter the one or more lens elements thereof. Thus, some type of opening must be provided in a housing used to mount such an assembly. This opening may reveal the very motion sensor assembly that is intended to be concealed from view.
Another problem associated with the design and construction of infrared motion sensor assemblies is that of standing waves. Surfaces of lenses and infrared detectors used in motion sensor assemblies are reflective. Improper positioning and alignment of these reflective surfaces can create standing waves of infrared energy. These standing waves can impair the sensitivity of the infrared detector because the detector receives these reflected standing waves in addition to infrared radiation from other sources. Another problem associated with infrared motion sensor assemblies results from the heating of the detectors used therein. Heating of an infrared detector due to the absorption of infrared energy radiated from one or more sources can impair the sensitivity of a detector due to its low thermal mass. Air currents caused by convection and other sources pose a further problem to infrared motion sensor assemblies. These air currents can affect the sensitivity of infrared detectors used in these assemblies. A final problem can result from the electrical circuitry used in connection with these infrared motion sensor assemblies. Infrared detectors used in motion sensor assemblies are of a high sensitivity. Microvolt level signals can affect the response from these detectors. Thus, noise in the electrical circuitry of a motion sensor assembly can adversely impair the proper functioning of an infrared detector used in the assembly.
An infrared motion sensor assembly that solved the above-described problems would be a welcome improvement. Accordingly, the present invention comprises a housing having an interior space bounded by at least one wall. At least one opening is present in the wall of the housing. An infrared detector and a lens are mounted in the housing such that the lens is adjacent the infrared detector and the opening in the wall. The lens focuses a field of view on the detector. When a source of infrared radiation moves across the field of view focused on the detector, the detector outputs a signal responsive to infrared energy radiated from the source. The detector, lens, and structure used for mounting them are concealed from view within the interior space of the housing by a radiation-permeable covering disposed in the opening. In one embodiment, the radiation permeable covering comprises a plurality of louvers. A circuit is provided that provides a signal in response to the output signal of the detector.
The lens and detector may be mounted adjacent one another through the use of a holder having a body and structure for receiving and securing both the detector and the lens. The receiving and securing structure for the detector may comprise a slot into which the detector is disposed. The receiving and securing structure for the lens may comprise a groove formed in a portion of the holder that receives a periphery of the lens. In one embodiment, the holder is a two-piece assembly having first and second pieces. The first and second pieces are matingly connected to one another. The mating connection comprises at least one plug formed on the first body piece that is received into a corresponding socket formed in the second body piece. The slot for receiving and securing the detector is formed on the first piece such that the slot is open on one end. A stop is formed on the second piece that abuts against the open end when the first and second pieces are matingly connected.
The lens and detector may be mounted in the housing so that a plane along a longitudinal length of the lens is offset from a plane along a longitudinal length of the detector so as to reduce internal reflection is between the lens and the detector. In one embodiment, the plane of the lens and the plane of the detector may be offset by approximately five degrees.
In one embodiment of the invention, the lens is a Fresnel lens having at least one lens element that focuses a field of view on the detector. In yet another embodiment of the invention, the lens may be a Fresnel lens that has five lens elements that focus five fields of view on the detector. At least one aspect of the combined field of view focused on the detector by this five element Fresnel lens is greater than 90.degree..
The holder of the motion sensor assembly may form a sink for infrared energy absorbed by the detector. Such a sink will absorb some of the heat energy absorbed by the detector.
The motion sensor assembly may further comprise a circuit board on which at least a portion of the circuit is mounted. The circuit board in this embodiment is secured to the housing. The mounting structure or holder used to receive and secure the lens and detector may have structure thereon for attaching the mounting structure or housing to the circuit board. The attaching structure may comprise at least one post integrally formed on the mounting structure or housing. The circuit board, lens, and body of the holder preferably forms a seal around the detector to shield the detector from air currents which can affect its sensitivity.
The motion sensor assembly may further comprise a transformerless direct current power supply for supplying power to the alarm signal circuit and detector. The transformerless direct current power supply is connected to an alternating current power source. The transformerless direct current power supply has a direct current common bus connected to a neutral conductor of the alternating current power source. The common bus and neutral conductor are both connected to earth potential.
The direct current power supply may have circuitry connected between an input of the direct current power supply and a line conductor of the alternating current power supply that shifts a phase angle of an alternating current drawn by the direct current power supply from the alternating current power supply. The alternating current is phase-shifted so as to be out of phase with an alternating voltage drawn by the direct current power supply from the alternating current power supply. The phase shifting circuitry reduces the real power consumed by the transformerless direct current power supply. The phase shifting circuitry may comprise a capacitor that is connected in series with the input of the direct current power supply and the line conductor of the alternating current power supply.
The circuit may comprise an amplifier having an input that receives the output signal of the detector, a comparator having an input electrically connected to an output of the amplifier, a load control having an input electrically connected to an output of the comparator, and a load, having an input electrically connected to an output of the load control. In one embodiment, the amplifier comprises first- and second-stages. The first-stage amplifies the output signal of the detector and low pass filters the output signal of the detector to reduce electrical noise. The output of the first-stage is capacitively coupled to the second-stage amplifier. The second stage amplifier amplifies the change in detector output caused by motion of the source in the field of view. The comparator compares a signal output of the amplifier to determine whether the signal output of the amplifier is within a range of values set by a voltage divider of the comparator. The comparator outputs a signal to the load control when the signal output of the amplifier is outside of the range of values set by the voltage divider. The load control comprises a timer, an input of which is electrically connected to an output of the comparator, so that the timer is triggered by the output signal of the comparator. An input of a triac is electrically connected to an output of the timer. An output of the triac is electrically connected to the load. The load may comprise a lamp.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.